Apparatus for heat treating lamp filaments



Sept. 27, 1966 J. J. MASON 3,

APPARATUS FOR HEAT TREATING LAMP FILAMENTS Original Filed April, 28, 1960 2 Sheets-Sheet 1 FIG-L H62. 300w 125% LAMP RATED VOLTAGE g5 c 125% LAMP RATED VOLTAGE 3| FIG. 4.

8Q 44 39 lg WOO W 39 L): l 5

I LAMP RATED VOLTAGE FIG. 6.

SINGLE FLASH FIG, 5, AT A.VOLTAGE BELOW T 300w RATED VOLTAGE (BALLASTED) 18 FIRST CHECK- 52 58 RELIGHTJ AT 51x -@2 FLASHING VOLTAGE 1 UNBALLASTED) 5o 48 [I00 w I25 "lo LAM P SECON D CHECK A. C, W RATED VOLTAGE FLASHING VOLTAGE ck T UNBALLASTED) 7 INVENTOR.

LAMP READY JULIEN I). MASON FOR ' BY SHIPMENTS: SALE 7 V S p 27, 1966 J. J. MASON 3,275,398

APPARATUS FOR HEAT TREATING LAMP FILAMENTS Original Filed April 28, 1960 2 Sheets-Sheet 2 L TRANSITION RANGE x EQUILIBRIUM RANGE'N 1',

FIG. 8

as E

RATE D voupez q TRANSlTlON RANGE l EQUIQIBRIUM RANGE b INVENTOR.

JULIEN .1. MASON.

AGE V United States Patent 3 Claims. (Cl. 316-27) This invention relates to electric lamps and, more particularly, to incandescent lamps having filaments with improved shock resistance and to a process and apparatus for flashing such lamps and heat treating the filaments thereof to effect the aforesaid improvement and minimize the degree of filament sag during flashing.

This application is a division of copending application Serial No. 25,285, filed April 28, 1960, now Patent No. 3,210,589, and entitled *Incandenscent Lamp and Process and Apparatus for Treating Lamp Filaments.

After incandescent lamps have been exhausted and sealed they are customarily lighted up or flashed a number of times at progressively higher voltages. The purpose of this socalled flashing schedule is to heat the filament to a sufliciently high temperature to vaporize impurities such as oxidies or other foreign matter that may be present on the surface of the wire and to convert such wire from its worked or fibrous microstructure to a crystalline microstructure that is conducive to good life performance. In lower wattage lamps where getter is applied to the filament to facilitate the cleaning up of gaseous impurities in the lamp, the aforesaid flashing also serves to vaporize such getter.

Flashing is most commonly accomplished on the hasing machine and a typical schedule for gas filled lamps having coiled-coil filaments consists of a step-wise increase of applied voltage from about 50% to 105% of the ratedlamp voltage in, perhaps, five or more index positions or stations of the basing machine. The flashing circuit at each of the aforesaid stations includes a suitable ballast (except in the case of low voltage lamps) to limit the current and thus prevent the impurities vaporized from the filament from causing an arc and mining the lamp. LA final light-up at 100% of the lamp rated voltage or higher is provided at an unballasted position for the purpose of detecting and destroying lamps having internals shorts.

As is well known, lamp filaments are fabricated from refractory metal such as tungsten that is produced by powder metallurgy techniques, drawn into wire and then wound into either a single coil or coiled-coil helix of the proper diameter and length. Thus, the filamentary wire before flashing has a worked or fibrous microstructure throughout and is, accordingly, sufliciently ductile to withstand the coiling operation. During flashing, the wire is heated to its recrystallization temperature and its fibrous microstructure thus converted to a crystalline microstructure with resultant setting or hardening of the filament. However, before the filament reaches its recrystallization temperature and is set and rendered sagresistant, it reaches a temperature at which it becomes plastic enough to sag under its own weight.

When the unflashed filament is slowly heated to its recrystallization temperature, as by flashing the lamp at progressively higher voltages in a plurality of steps in accordance with conventional flashing schedules, the filament remains plastic for a sufliciently long period of time to develop an appreciable amount of sag. While the degree of sag which occurs during multiple-step flashing may not be serious in lamps having filaments that are disposed transverse to the lamp axis, as for example in 3,275,398 Patented Sept. 27, 1966 the so-called C9 or CC6 type filament, it constitutes a serious problem in the vertically mounted coiled-coil or CC8 filaments now being employed in that when such lamps are flashed in a vertical position it causes the spacing between the secondary turns at the lower end of the coil to decrease and the spacing between turns at the upper end of the coil to increase. The resultant nonuniform temperature distribution along the length of the filament produces hot-spots which shorten the life of the lamp and cause undesirable variations in its rating. As a solution to this problem it has been proposed that lamps having CC8 filaments be flashed in a horizontal rather than a vertical position. However, this is not only inconvenient from a manufacturing standpoint but produces an appearance defect in lamps with clear bulbs since the coil sag is asymmetrical to the lamp axis rather than symmetrical as in the case of C9 and CC6 filaments.

In addition to the aforesaid sag problem, the .prior art practice of completely recrystallizing the filament during flashing makes it brittle and very fragile. As a result, the filament frequently breaks while the finished lamp is being packed or shipped thus posing a problem that has plagued the lamp industry from its very inception and, in some cases, necessitates the use of very costly packaging.

It is according the general object of this invention to provide apparatus for processing unflashed incandescent lamps that will avoid the foregoing and other problems of the prior art.

A more specific object is the provision of means for producing a lamp filament that has a microstructure after flashing which improves the shock resistance of the filament and reduces the incidence of filament breakage during hand-ling and shipment of the finished lamp.

Still another object is to provide apparatus for flashing incandescent lamps and heat treating the filaments thereof which will produce the aforesaid microstructure and substantially reduce the degree of filament sag during flashing.

The foregoing objects, and others which will become apparent as the description proceeds, are achieved by providing a flashing circuit which permits the lamp to be flashed in a single step or operation instead of in several stages as heretofore. A voltage of such character is applied to the lamp that the filament is rapidly heated to its recrystallization temperature and set. Thus, the filament is in a plastic condition for a shorter period of time than in the case of the prior art mode of flashing and accordingly experiences less sag.

According to the second aspect of this invention, the incidence of filament breakage during shipment of the finished lamps is reduced by employing a circuit wherein the flashing voltage has an equilibrium value below that at which complete recrystallization of the filament would occur within the flashing period. The flashed filament is, accordingly, only partly recrystallized or underflashed and has unreerystallized fibrous regions therein which render the flashed filament more resilient and better able to withstand the vibration and shock it experiences during the packing and shipping of the finished lamp. Preferably, the two concepts, namely, underflashing and onestep flashing, are combined to provide a flashing circuit which controls both the degree of filament sag and brittleness or fragility which occur during flashing.

For a better understanding of the invention, reference should be had to the accompanying drawings wherein: FIG. 1 is an elevational view of a 300 Watt PS30 incandescent lamp incorporating a coiled-coil CC8 filament processed in accordance with this invention;

FIG. 2 is a schematic diagram of one type of flashing circuitthat can be employed in accordance with FIGS. 3 to 5 areschematic representations of other and preferred types of flashing circuits wherein one or several incandescent lamps are employed as the ballast means;

FIG. 6 is a block diagram illustrating a preferred sequence. of steps-according to the invention for completing the fabrication of an incandescent lamp and inspecting it prior to shipment; and,

FIGS. 7, 8 and 9 are graphic representations of the flashing voltages obtained from the circuits illustrated in FIGS. 2,3 and 5 respectively.

While the present invention can be advantageously employedin the manufacture of various types. of incandescent lamps, it is particularly adapted for use in conjunction With incandescent lamps having vertically mounted coiled-coil filaments and has accordingly been so illustrated and will be so described.

With specific reference to the form of the invention illustrated in the drawings, inFIG; 1 there is shown a 300 watt CC8 incandescent lamp 15 which generally comprises a pear-shaped envelope .16 having a coiledcoiled filament 18 sealed therein and supported in sub stantiallyooaxial relationship therewith by a pair of lead-in conductors 19 and 20 and the usual support and tie wire arrangement. The aforesaid conductors are sealed through a conventional re-entrant glass stem 22 1 that is fused to the end of the envelope neck and protrudes inwardly therefrom. Electrical connection with the lead wires and filament is effected in the usual manner by means of a base 21 attached to the sealed end of the envelope. Thelamp 15 contains a filling of suitable inert gas such as a mixture of 90% argon and 10% nitrogen, for example, at a pressure of 600 millimeters of mercury.

The filament 18 is fabricated from a suitable refractory metal wire such as wire consisting essentially of tungsten, for example, that has been prepared in accordance with standard powder metallurgy techniques. -As a specific.

example; tungstic acid or tungstic oxide is firstprepared from tungsten ore and has added thereto predetermined amounts of so-called doping compounds, such as silicon dioxide, alumina, and potassium chloride, for example, to form a slurry that is then chemically reduced to metallic tungsten powder. The powder is then compacted and sintered to form an ingot that 'is mechanically Worked, as by swaging or drawing, into afilamentary wire of the desired diameter. The wire at this stage is ductile and hasthe characteristic fibrous or stringy microstmcture of worked unrecrystallized wire. Photomicrographs have shown that the filamentary wire initially (that is, prior to flashing) is of fibrous microstructure throughout.

In the Metals and Alloys Dictionary by M. Merlub- Sobel, Chemical Publishing Company, In'c., N.Y. 1944, the word fiber is defined as the direction in which metals have been caused to'flow, as by rolling, with miacroscopic evidence in the form of fibrous appearance in the direction of flow, and .the expression fibrous structure defined in terms of a fibrous fracture having a surface of long stringy nature. The word fibrous as herein used accordingly refers to a stringy pattern or structure in the wire as distinguished from a granularv Fibrous regions as used herein accordingly denote unrecrystallized regions in the filaor crystalline structure.

between about 40% and 75% of the lamp rated voltage (13,), or approximately 2000-2500. K. The unflashed lamp is, accordingly, energized with a voltage of such magnitude that the filament is rapidly and continuously heated through the aforesaid temperature range to the desired equilibrium temperature- In accordance with the second aspect of this invention, it has been found that the strength of the filamentcan also be improved by maintaining theequilibrium .value (E of the applied flashing voltage between about 75% and E Voltages of this order will heat the filament sufficiently to set it with a minimum of sag without oompletely recrystallizing it within the flashing period. Good results have been obtained in the case of the 300 watt CC8 .la'mp here illustrated by maintaining the equilibrium value Thus, by controlling both the rate of rise of temperature.

of the filament and its ultimate or steady. state temperature, the filament can be set with a minimum amount of sag without causing the complete recrystallization and em-brittlement-thereof. The aforesaid voltages and'ranges.

are merely illustrative and will vary depending upon the particular type of lamp .andfilament involved.

Various types of flashing circuits for heat treating un flashed filaments in accordance with the foregoing .will now be described.

In FIG. 2 there is shown a resistor-ballasted flashing circuit according to the invention wherein a current-lirnite ed voltage of predetermined magnitude is applied to a lamp 15.by meansof a pair of conductors25 and 26 that connect the lamp to an AC. voltage source through a v-ariable'resistor '28 and "a switch 30 that are connected in series with each other andthe lamp filament 18.3 The magnitude of the supply voltage exceeds the" lamp rated voltage (E,') by a predetermined amount, as for example,

125% E as in ,the case of a 300 watt CC8 volt lamp here shown. equilibrium value of the voltage (E which appears across the filament 18.:during flashingisset. at a predetermined value high enough to heatthe filament to its recrystallization temperature and set it, but lowenough to prevent the complete recrystallization thereof within the flashing period, as for. example, 80% E. as mentioned above.

Under these conditions, whenthe switch 30 is closed and an unflashed 300 watt CC8 lamp 15 isin the circuit,

a voltage in the order. .of 16% B, will be immediately applied to the filament 18 which voltage rises to 73% E 1 in about twenty cycles. The resulting wave form of the flashing voltage appliedto the lamp is shown in :FIG. 7.- As will be noted, the transient portion of the :flashing voltage (that is, the region a-b in FIG. 7) is such that the voltage across the filament rises fairly rapidly from its. initial relatively low value to its equilibrium value Egor 80% E Thus, the filament temperature is continuously.

increased and traverses the. critical sag temperature range in a much shorter time than in the case ofja conventional multiple-step flashing schedule.

The actual rate at which the filament heats up will, of

course, vary considerably. depending .upon the particular type of lamp, wire size, coil design, fill gas, etc. involved:

However, in order to effectively limit the amount ofisag during flashing with most coiled filaments, the. filament should reach'a temperature of about 25.00" K. within three seconds afterthe voltage is applied. It would, of

course, be preferred if the filament were heated to this temperature in a shorter time interval since this would reduce filament sag still further.

A circuit capable of achievingboth underflashing and accelerated heating of the filament is shown in .FIG. 3.

wherein a pair ofincandescent lamps 34 and 36 arranged in parallel constitute 'the ballastimeans. Asshown the By properly adjusting the resistor 28 the i lamps 34 and 36 are connected between one end of the unflashed filament 18 and one side of the voltage supply by means of a conductor 32 and a switch 38. The other end of the unflashed filament is connected to the other side of the supply line by another conductor 31 as before. In order to enable the unflashed filament 18 -to heat up faster than the filaments of the ballast lamps 34 and 36 it is necessary that the combined wattage of the ballast lamps be greater than that of the unflashed lamp and the proper balance of impedance thus provided. In the particular case of an unflashed 300 watt CC8 lamp 15 here shown, this is accomplished by using a pair of 200 watt lamps as the ballasting means.

If the A.C. supply voltage is 125% E as indicated in FIG. 3, the voltage applied across the unflashed filament 18 by this particular circuit will have a wave form of the character shown in FIG. 8. As there shown, upon closure of the switch 38 the initial voltage applied to the unflashed filament 18 is about 75% 13,. The voltage rises to approximately 93% E,- in about seven cycles, and then gradually decreases to 86% E in thirteen cycles and finally to its equilibrium value E or 80% E,. It should be noted that in this case the transient (that is, the region a to b in FIG. 8) by virtue of the non-linear resistance of the ballast lamps is such that the voltage applied to the unflashed filament first exceeds and then decreases to its preselected equilibrium value E Thus, the unflashed filament is heated to its recrystallization temperature at a faster rate than withthe resistor-ballasted circuit described above and is thus set with a minimum of sag.

In FIG. 4 there is shown essentially the same type of circuit as illustrated in FIG. 3 except that a single lamp 42 is used as the ballasting means. This type of circuit is of particular use where the wattage of the lamp 15a is such that the impedance balance necessary to achieve accelerated heating of the unflashed filament 18a to the desired temperature can be obtained by using a ballast lamp of a standard and hence readily obtainable wattage. In the example here shown, the unflashed lamp 15a is a 200 watt CC8 lamp and the ballast lamp 42 has a 300 watt rating. As before, the ballast lamp 42 is connected in series with one end of the unflashed filament 18a and one side of the voltage supply through a conductor 39 and switch 44, and the other end of the unflashed filament is connected to the voltage source by'means of another conductor 40. For the particular combination of lamps and supply voltage here shown, the wave form of the voltage appearing across the unflashed lamp 15a would be similar to that shown in FIG. 8, except that because of the less massive filament being treated the applied voltage would reach its equilibrium value in a shorter time.

Heating of the unflashed filament can be achieved at an even faster rate by preheating it to a temperature below its recrystallization and sag temperature before flashing in order to increase its initial resistance. A circuit of this character is shown in FIG. 5 wherein a 300 watt CC8 120 volt lamp 15 is connected to the supply voltage by means of a preheating circuit consisting of conductors 45 and 46, a switch 50, and a 100 watt ballast lamp 48 which is connected in series with the unflashed filament 18 and one side of the line. When the switch 50 is closed and the unflashed lamp 15 is connected to an A.C. supply voltage of 125% E as here shown, the ballast lamp 48 limits the current through the unflashed lamp, to a value such that a voltage drop E (see FIG. 9) of about 17 volts or 14% E appears thereacross. This is suflicient to substantially increase the resistance of the filament 18 but is well below the critical range of 40 to 75% B in which filament sag occurs.

After the unflashed filament 18 has been preheated, three additional 100 watt ballast lamps 54, 56 and 58 are connected in parallel with the first ballast lamp 48 by means of conductors 51 and 52 and a second switch 60. Thus, the ballast lamp 48 is first utilized to limit the current in the preheat circuit and is then used as part of the multiple-lamp-ballasted flashing circuit formed when the aforesaid preheating circuit is connected to the network of parallel-connected ballast lamps 54, 56, and 58. As will be noted in FIG. 9, the voltage is at a maximum initially and then decreases to an equilibrium value of about E,.. The peak initial voltage in the case of the volt 300 watt lamp 15 shown is in the order of volts. Thus, upon closure of the switch 60 (represented in time .by the ordinate a" in FIG. 9) the voltage immediately increases from the low preheating voltage E to a value higher than E (in this particular case about 108% the aforesaid equilibrium voltage B In FIG. 6 there is shown a preferred series of steps for flashing and inspecting incandescent lam-ps preparatory to shipment in accordance with the invention. As shown, the lamps are first flashed in a single step or operation at a ballasted position and at a preselected voltage below the lamp rated voltage to set but not fully recrystallize the filaments. Preferably, the flashing voltage is about 80% of the lamp rated voltage and is applied for a period of about 2 to 3 seconds. After flashing the lamps are relighted twice at 'unballasted positions for about the same length of time and at a voltage no greater than that at which they were flashed, and preferably at the same voltage. In this manner lamps having arc-initiating defects are detected and destroyed before shipment Without substantially increasing the degree of recrystallization of the filaments of the good lamps. The lamps which pass inspection are then packed and shipped. Completion of the recrystallization process within the filament is achieved when the lamp is subsequently lighted at its rated voltage in the customers socket.

It has been found advantageous in practice to provide two or more separate flashing circuits on the basing machine and to switch from one set to the other. Otherwise, the filaments of the ballast lamps may not have sufiicient time to cool while the machine is being indexed and hence may have too high a resistance.

Photomicrographs of 300 watt coiled-coil filaments re moved from lamps that were flashed in a single step in accordance with the invention at a voltage having an equilibrium value of about 80% of the lamp rated voltage have shown that the wire is composed of discrete grains of irregular configuration joined by unrecrystallized fibrous regions. This structure extends throughout the entire length of the wire so that a plurality of discrete fibrous regions and grains intermingled one with another are actually present therein. Both the grains and fibrous regions are elongated in the general direction of the wire axis with the latter substantially filling the crevices in the irregular surfaces of adjacent grains which they join thereby constituting, in effect, a resilient bridge or link therebetween. In an underflashed filament, accordingly, substantial portions of adjacent grains are joined by unrecrystallized fibrous regions thereby eliminating the clearly defined or discrete grain boundaries normally observed in fully recrystallized wire produced by conventional flashing circuits.

Comparative tests have shown that lamps flashed in a plurality of stages at progressively higher temperatures in accordance with conventional practice are fully recrystalv lized and have the same microstructure after flashing as they have after being seasoned, whereas identical lamps flashed only once at a preselected voltage below their rated voltage in accordance with this invention have a distinctly different microstructure that improves the shock resistance of the filament and is totally different from the fully recrystallized structure observed after seasoning.

In the specific case of the 300 watt CC8 lamp here shown, the filament sag due to flashing has been reduced by approximately 50% when the one-step flashing schedule of this invention was employed. In addition, drop tests on comparative lots of conventionally flashed lamps and lamps underflashed in accordance with the principles of this invention have shown that the incidence of coil breakage is reduced by a factor of about to 20,

that is, one broken underflashed filament for every ten to 1 twenty regularly-flashed filaments fractured.

As will be apparent from the foregoing, the objects of the invention have been achieved by providing apparatus for flashing incandescent lamps and controlling the heat treatment of the filaments so that the filaments experience a minimum amount of sag during flashing and are provided with a shock-resistant microstructure.

While specific examples of various flashing uircuits of the invention have been illustrated and described, :it will be understood that various modifications and changes can means in series with the filament of said nnfla'shed lamp and one side of said voltage source; and (2) a second cir cuit including a ballast lamp, second conductor means, and a second switch for connecting said second circuit in parallel relationship with the current-limiting means in said preheating circuit; the impedance of said currentlimiting means being such that the current flowing through said'unflashed lamp, when said first switch is closed, is

suflicient to heat'the filament thereof to a predetermined.

temperature below its recrystallization and sag temperature and thus increase the resistance of said filament; said preheating circuit and said second circuit when connected comprising a flashing circuit the total impedance whereof is greater than that of saidunflashed lamp. 7

2.3 Apparatus for heat treating the filament of an unfiashed incandescent lamp as set forth in claim 1 wherein;

said current-limiting means comprises a second ballast 1 lamp having a Wattage rating less than that of the .un-

flashed lamp, and said ballast. lamps' have a total wattage rating greater than that of said unfiashed lamp.

3. Apparatus for flashing a 300 wattincandescent lamp comprising, a first circuit connecting said 300 watt lamp;

to a voltage source, andin .series with a watt incandescent ballast lamp, and a second circuit including a,

network of three parallel-connected 100 watt incandescent lamps and a switch operable to ,connectsaid network of ballast lamps in parallel relationship with the 100 watt ballast lamp in said firstcircuit.

References Cited bythe Examiner 1 UNITED STATES PATENTS 397,906 2/1889 1 Galvin 315 192;X 1,234,028 7/1917 Housbeiger 315 192x- 1,540,307 6/1925 Beall. 2,069,407 2/1937 Fonda 316-1 x 2,440,537 4/1948 Belar 315 179 FRANK E. BAILEY, Primary Examiner. 

1. APPARATUS FOR HEAT TREATING THE FILAMENT OF AN UNFLASHED INCANDESCENT LAMP HAVING A PREDETERMINED RATED VOLTAGE AND RESISTANCE, WHICH APPARATUS COMPRISES; (1) A PREHEATING CIRCUIT INCLUDING A VOLTAGE SOURCE THAT EXCEEDS THE RATED VOLTAGE OF SAID UNFLASHED LAMP BY A PREDETERMINED AMOUNT, CONDUCTOR MEANS FOR CONNECTING SAID LAMP TO SAID VOLTAGE SOURCE, CURRENT-LIMITING MEANS, AND A FIRST SWITCH ARRANGED TO CONNECT SAID CURRENT-LIMITING MEANS IN SERIES WITH THE FILAMENT OF SAID UNFLASHED LAMP AND ONE SIDE OF SAID VOLTAGE SOURCE; AND (2) A SECOND CIRCUIT INCLUDING A BALLAST LAMP, SECOND CONDUCTOR MEANS, AND A SECOND SWITCH FOR CONNECTING SAID SECOND CIRCUIT IN PARALLEL RELATIONSHIP WITH THE CURRENT-LIMITING MEANS IN SAID PREHEATING CIRCUIT; THE IMPEDANCE OF SAID CURRENTLIMITING MEANS BEING SUCH THAT THE CURRENT FLOWING THROUGH SAID UNFLASHED LAMP, WHEN SAID FIRST SWITCH IS CLOSED, IS SUFFICIENT TO HEAT THE FILAMENT THEREOF TO A PREDETERMINED TEMPERATURE BELOW ITS RECRYSTALLIZATION AND SAG TEMPERATURE AND THUS INCREASE THE RESISTANCE OF SAID FILAMENT; SAID PREHEATING CIRCUIT AND SAID SECOND CIRCUIT WHEN CONNECTED COMPRISING A FLASHING CIRCUIT THE TOTAL IMPEDANCE WHEREOF IS GREATER THAN THAT OF SAID UNFLASHED LAMP. 